Data Types and Modules

Data Types and Modules

Data Types

Visual Basic supports different types of data types according to the needs of program or application

You can say that attribute of a variable that determines what kind of data it can hold is known as Datatype.

By Default Visual Basic supports the variant data type.Declaring a variable variant indicates that it can support all types of data types.Mainly Visual Basic supports the following datatypes:

Table of Data Types

Data Types Storage (in bytes) Prefix Example Byte 8 Byt bytVar Boolean 1 Bln blnNum Integer 2 int intCount Long; 4 lng lngNumbers Single 4 sng sngAverage Double 8 dbl dblMarks Date 8 dte dteNext Object 4 obj ObjMywork Avgs String According to the length of string str strNames Variant 16 vnt vntTotal

Data Types and Modules   Variables   Any programming language requires to store values temporarily for different purposes like calculations Adding, multiplying etc.Visual Basic gives the need for variables. You can think of variable, a place in memory of computer for an unknown value. For example when you call someone, then you call him /her by name, like that every variable has name. Variable name is the word which you use to refer to the values that the variable contains.   VARIABLES:- Naming convention   There are different rules for assigning names to variables ,these are as follows:   A variable name must begin with a letter.   For example: 6date - Invalid variable name date6 - valid name   Two variables must not contain the same name.   It can not contain a dot or space.   For example: Num2 - Valid variable name Num.2 - Not Valid Num 2 - Not Valid   A variable name must not exceed 255 chracters.   A variable name must not contain any special characters like %, $ , * , & ,! ,@ etc.   For example: @num, num$r are not valid variable names.   Variable:-Declaring   The term declaring a variable means that the memory is allocated .This memory will be referred by a name decided by the programmer.The specific data type decides the amount of memory allocated. You can declare a variable with a Dim statement by giving a name for the variableaccording to rules of naming conventions.   Syntax: Dim variablename as Datatype   Example: Dim a as integer In above example 'a' is variable name and integer is the data type.   Rules for declaring variables: (i) Declaring a variable using the word Public makes it available throughout the program. (ii) Declaring a variable using the word Static keeps it's value preserve until a procedure ends. (iii) Declaring a variable in the declaration section of the form makes it available to all procedures in that module.   For example: Let us consider the variable 'var1 '. An integer variable 'var1' is declared. At the same time memory is allocated for the variable. The variable is given value 20 during the running state of the program. This value is stored in the given memory location.   This process is shown in figure:           Data Types and Modules   Constants   Constants as the name suggests , never change during the execution of program.They remain same throughout the program execution. When the user wants a value that never changes, a constant can be declared and created.   The syntax for declaring a constant is:   (Public|Private) Const constantname (As type) = expression   The const statement can be declared as:   Public const pie as single=3.14           Data Types and Modules   Modules   A module is a set of functions and a set of data members.Code in Visual Basic is stored in the form of Modules. Collection of general procedures, variable declarations, and constant definitions used by application is known as module.   Mainly Visual Basic supports 3 types of modules:   (1) Form module (2) Standard Module (3) Class Module   Form module   Form modules provide the user interface to the application. They contain controls and properties of the forms. They have the extension .FRM. Their declaration is private by default, therefore each form has a single form module associated with it.   Standard Module   As we go further in developing the application than there may be common code for execution of several form. For avoiding the duplication of code, a separate module containing the code is implemented. This is called as standard module. A standard module (.BAS) contains only code. It contains extension .BAS.   Class Module   A class module (.CLS) is used to create objects (forms etc.). It can be called from procedures within your application. Class modules (.CLS filename Extension) are writing code in class modules can create the building blocks of object oriented programming in Visual Basic.New objects.   Each module contains different elements, these are:   Declaration It includes constant and procedures.   Procedures Sub function or property procedures that contain pieces of code that can be executed as a unit. It avoids code repetition.